Process of recovering tin



July 15, 1924.

ALAN KISSOCK, OF LOS ANGELES, CALIFORNIA.

PROCESS OF RECOVERING TIN.

No Drawing.

To all whom it may concern:

Be it known that I, ALAN KISSOCK, a citizen of the United States, residing at Los Angeles. in the county of Los Angeles and State of California, have made certain new and useful Improvements in Processes of condltions of Recovering Tin, of which the following is a specification.

The invention relates to a novel detinning process, that is, a process. for recovering the tin coating from what is usually known as tin scrap.

The invention consists in the novel steps, sequence of steps, sub-processes and processes herein described. The objects and ad vantages of the invention will beset forth in part hereinafter and in arent to those skilled in the art, or may learned by practicing the invention.

In commercial work the tin scrap usually comes in bales, and a. concrete or iron vat or somewhat shallow tank is usually employed for the first or chemical part or step in the process.

In carrying out my process the tin scrap is immersed in an alkaline polysulfide solution and at the present time I preferably employ sodium polysulfide, largely for economic reasons. This solution in my present practice consists preferably and approximately of 4 pounds of sodium polysulfide dissolved in about 2 gallons of Water, although these proportions under different practice may be varied very widely.

By the action of this solution on the tin scrap, the tin coating is completely dissolved from its sheet iron or sheet steel base, with the formation of a soluble alkali thiostannate.

The reaction is probably as follows Although iron and steel are ordinarily unattacked by such alkaline sulfide solutions,

usually in practice a. certain small proporreadily oxidizes to a basic iron sulfate.

To recover the metallic tin from the alkali thio-stannate solution, when the solutlon as i made up has become, through the operation part will be ap- Application filed June 15, 1921. Serial No. 477,788.

of the process, impregnated with the tin to its full or to a sufiicient extent, the basic iron sulfate is separated from the solution by filtration. and the clear solution of alkaline (in the present instance, sodium) thiostannate is electrolyzed by means of a low voltage current.

The anode or anodes employed are preferably of insoluble or substantially insoluble material, such as iron or graphite, and the cathode or cathodes are preferably of sheet tin, the tin from the solution being deposited on the tin cathodes. These cathodes are later melted and cast into pure block tin ingots.

The principal reaction is probably substantially as follows Solution NaaSnS;

Cathodic Anodic Sn de ited Na a ars but is S appears but immediately disimmediiiigly wou d; solves according to either 0! lollowing reactions Na+H10=Na0H+H N a:S=+S=-Na:Sx+1

' 2N8oH+s.-Na.s.+mo+o thus regenerating solvent.

The secondary reactions occurring during the electrolysis cause the appearance of sulfur at the anode, which is again dissolved by. or recombined with, the alkali hydrate formed at the cathode. In this way, during the process of recovering the tin, the alkaf line polysulfide is regenerated, and the thus regenerated solution is ready for the treatment of fresh tin scrap.

The regenerative reaction of the solution just described, is probably substantially as follows Same as immediately secondary reactions,

The process may employ the polysulfide solution either hot or cold, and the solution may be'concentrated or diluted, these factors or conditions only or mainly afiecting the rapidity of the reaction, and it will be understood that the proportions given hereinbefore are merely illustrative of what is now regarded as good commercial practice.

Notwithstanding the regenerative feature of the process, addition of fresh chemicals must be made from time to time to compensate for the mechanical losses of the solution due to dipping the scrap and other features of handlin The tin scrap after being subabove or eliminating jected to t e polysulfide bath whereby the tin coating is removed therefrom, is washed to remove from such de-tinned scrap the tin-- bearing solution.

The process is simple, rapid, relatively in-' expensive and regenerative, besides possessing other advantages. It will be understood that changes may be made in the manner of practicing the invention within the scope of the appended claims without departing from the rinciples of the invention and, without sacrificing its chief advantages.

What I claim is 1. The process of recovering tin from tin scrap which comprises acting on the tin scrap by an alkaline polysulfide solution to create an alkali thio-stannate solution and electrolyzing the alkali thio-stannate solution to deposit the tin from the solution,

and thereby regenerating the solution to produce a polysulfide for use in the first step of the process.

2. The process of recovering tin from tin scrap which com rises actin on the tin scrap by create an alkali thio-stannate solution and electrolyzing the alkali thio-stannate solu-.

tion by using a substantially insoluble anode to deposit the tin from the solution, and thereby freeing the tin and regenerating-the polysulfide for use in the first step of the process.

3. The process of recovering tin from tin scrap which comprises treating the tin scrap with an alkaline polysulfide solution to reduce the tin of the scrap to a dissolved thio-stannate, electrolytically depositing the tin from the thio-stannate solution and thereby regenerating the polysulfide solution for use in the first step in the process.

In testimony whereof, I have signed my name to this specification.

ALAN KISSOCK.

an alkaline polysulfi e solution to 

